The present invention generally relates to systems, apparatus, and methods related to eye surgery. More particularly, the present invention relates to systems, apparatus and methods for cataract surgery. Cataract surgery is one of the most common ophthalmic surgical procedures performed. The primary goal of cataract surgery is the removal of the defective lens and replacement with an artificial lens or intraocular lens (IOL) that restores some of the optical properties of the defective lens.
The major steps in cataract surgery consist of making cornea incisions to allow access to the anterior chamber of the eye and to correct for astigmatism (Limbal relaxing incisions, LRIs), cutting and opening the capsule of the lens to gain access to the lens, fragmenting and removing of the lens and in most cases placing an artificial intraocular lens in the eye.
The cornea incisions are typically performed with surgical knives or more recently with lasers.
Cutting of the capsule is most commonly done through skillful mechanical cutting and tearing a circle shaped opening, using hand tools. This procedure is called capsulorhexis.
Traditional methods for performing a capsulorhexis are based on mechanical cut and peeling techniques. Another method referred to as YAG laser anterior capsulotomy delivers individual laser pulses with high energy to the eye to assist with the opening of the capsule. The precision and quality of these methods is limited.
More recently, photodisruptive lasers and methods have been introduced that can perform the capsulotomy/capsulorhexis opening cut with great precision. The inventor's prior patents and patent applications regarding photodisruptive lasers for use in eye surgery include: U.S. Pat. Nos. 6,992,765 and 7,371,230; and U.S. patent application Ser. No. 12/902,105 and PCT/US11/54506. Photodisruptive laser pulses in the range of <10000 femtoseconds have been successfully applied to make incisions into various tissues of the eye. The main focus to date has been using a femtosecond laser for various cornea incisions such as LASIK flaps, intrastromal incisions, Limbal Relaxing Incisions, Keratoplasties and cornea entry incisions. In more recent years femtosecond lasers have also been successfully applied to the capsule and the lens of the human eye in femtosecond laser assisted cataract procedures.
The main benefit of these photodisruptive laser pulses lays in the fact that the eye tissues that are treated transmit the wavelengths of the typically chosen lasers, usually in the near infrared or visible range and therefore allow the laser to be focused through the cornea, aqueous humor, lens capsule and lens without much scattering or absorption. The laser pulses are always focused to a very small spot size in the range of a few micrometers, so that a laser induced optical breakdown is achieved in any tissue or liquid (e.g. aqueous humor) that falls within the spot size location.
This optical breakdown (photodisruptive breakdown) creates a micro plasma followed by a small cavitation bubble. This photodisruption of tissue can be used to cut and dissect tissue areas of any size and shapes by scanning a sequence of many such laser pulses over a desired volume in the eye.
Since the tissue layers in the laser path above and below the focus point are below the optical breakdown threshold and since they don't significantly absorb the laser wavelength, they remain unaffected by the laser beam. This principle allows non-invasive photo disruptive eye surgery since no incision from the outside needs to be made.
There is a threshold of a minimum laser fluence (laser peak power divided by focus area) required to achieve the optical breakdown. The laser peak power goes up with higher pulse energy (typically in the μJ range) and shorter pulse duration (typically <600 fs). The laser fluence for any given peak power goes up as the focus area goes down. Achieving a small spot size is therefore critical in achieving a high fluence that exceeds the optical breakdown threshold.
The way of achieving a high enough fluence for breakdown by increasing the laser pulse energy is less desirable since a higher pulse energy comes with a larger cavitation bubble and associated shock wave. The larger the cavitation bubble the less precision is achieved in cutting any features with a sequence of pulses. Furthermore a large shock wave is considered a undesired side effect since it has the potential to damage surrounding tissues.
Priority is therefore given to minimizing the spot size to achieve an above threshold laser fluence while using laser pulses within a low pulse energy range of typically <50 μJ per laser pulse. These principles have been successfully implemented in femtosecond eye laser systems treating the cornea or capsule/lens of an eye. Typical laser beam focusing convergence angles required are numerical apertures of NA>0.15 (full angle Φ>15 deg) and in some optimized cases NA>0.3.
According to:ω0=M2360λ/π2Θ  Formula 1
Φ=full focusing convergence angle in degrees
λ=laser wavelength
ω0=laser beam focus radius defined by 1/e2 cut off
M2=beam quality factor determined by the total aberrations
If beam aberrations can be kept to a minimum e.g. M2<1.3 (M2=1 is the theoretical minimum with no aberration at all) then the above focusing angles of NA>0.15 (Φ>15 deg) and NA>0.30 (Φ>30 deg) the resulting spot size diameters (2ω0) will be <8 μm and <4 μm respectively (for a laser wavelength λ=1 μm).
The high numerical aperture and minimization of aberrations is critical in achieving such small spot sizes. The laser delivery systems for such laser parameters face several challenges due to the high numerical aperture required to achieve a very small spot size. These systems get further complicated by using a laser beam that is scanned through the focusing lens assembly. Maintaining low aberration while scanning a laser beam at an incidence angle other than normal (90 degrees of incidence) through a lens that creates a high numerical aperture focused beam, requires a complex system of multiple lenses in a precise arrangement. Additionally, those methods and systems require a patient interface such as an applanation lens to reference and fixate the eye to the laser system. Placement of this patient interface adds significant complexity to the surgical setup and can cause undesired or harmful high intraocular pressures for the duration of the laser procedure. The patient interface is typically provided sterile and is used only once therefore adding significant cost to the overall cataract procedure. Additionally, no current patient interface or laser delivery system that can perform the laser cornea incisions and laser capsulotomy is compatible or has been integrated with a standard surgical microscope. Since the cataract surgery requires a surgical operating microscope to be completed, the patient must be moved and repositioned under a surgical microscope after the current laser assisted parts of the procedure have been completed. This causes a significant time delay and logistical effort.
The delivery system, disclosed herein, avoids such a complex focusing lens setup by implementing a specific laser scanning design that allows the focusing lens to always remain under normal incidence (90 degrees) to the incoming laser beam(s). This dramatically reduces the delivery system size, complexity and induced beam aberrations. Furthermore, several novel delivery system integration designs are disclosed that allow a femtosecond laser treatment with or without a patient interface to be integrated with a standard surgical microscope. This application describes, among others, techniques, methods, apparatus and systems for laser based cornea incisions and capsule perforations (capsulotomy) to create an easier capsulorhexis procedure. Implementation of the described techniques, apparatus and systems include: determining a surgical target region in the cornea and anterior capsule of the eye, and applying laser pulses to photo disrupt a portion of the determined target region to create an opening cut on a cornea or capsule of the lens.